Glass melting furnaces are refractory lined vessels shaped as containers for melting and holding glass. In the melting operation, the incoming glass making materials are heated to about 2800° F. (1550° C.). The glass-making materials usually include a mixture of cullet and batch materials. Cullet is crushed glass from the manufacturing process. Batch materials include sand (silica), lime (limestone or calcium carbonate reduced to calcium monoxide), soda ash (sodium monoxide), and sometimes other materials such as feldspar, salt cake, and metal oxides. During the melting operation, the cullet melts first to increase the heat transfer to the batch materials and to reduce the melting time.
Glass melting furnaces include pot furnaces, glass tanks, tank furnaces, and the like. Pot furnaces have a crucible or bowl shape configuration and typically are used to melt smaller quantities of glass. Glass tanks range from smaller day tanks to larger continuous melt tanks. Day tanks are usually filled with glass making materials for overnight melting. Continuous melt tanks are large furnaces where glass making materials are charged at one end, melt, and flow to the other end for removal. Glass tanks typically are constructed of separate refractory brick or blocks within a steel frame. The blocks fit together without mortar and typically are arranged in a rectangular shape to hold molten glass. The mechanical pressure from the steel frame and outer blocks holds the blocks together. Glass tanks generally have regenerative chambers to preheat combustion air for higher flame temperatures.
The refractory blocks usually receive considerable wear from the molten glass and the charging of glass making materials. Molten glass is highly corrosive. The refractory blocks usually are made of composite clays having alumina, zirconia, and silica (AZS). The AZS refractory blocks are made from molten material cast into molds, which are machined after hardening.
The melting operation in continuous melt tanks continues essentially non-stop until the tank is no longer usable. During the melting operation, the refractory blocks can become deeply scored and may develop wear spots or portions where the molten glass has eroded or dissolved the refractory. The wear spots typically grow until the refractory fails to hold the molten glass. The wear spots shorten the service life of glass tanks and often are unpredictable, thus disrupting production of molten glass.